Selective metal accumulation by metal-resistant bacteria growing on spent engine oil in single and ternary metal mixtures
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Three metal-resistant bacteria species, identified as Pseudomonas alcaligenes B101, Pseudomonas fluorescens C101 and Stenotrophomonas maltophilia E103, isolated from spent engine oil-contaminated tropical soils utilised spent engine oil (SEO) as a source of nutrient for growth in the presence of Pb2+ (500 µg/ml), Cu2+ (400 µg/ml) and Zn2+ (400 µg/ml) with concomitant cellular accumulation of the metals in single and ternary mixtures. Degradation of SEO in the presence of the metals and their mixture within a 21 days experimental period ranged between 27.8 and 57.8% compared to 52.2% and 66.7% in metal free controls with extensive modification (up to 92.7%) of the aromatic fractions of the spent oil. Cellular accumulation of the metals during SEO degradation ranged between 0.13 and 30.76%, and 3.77% and 33.43%, respectively, in growth media supplemented with single metal ions and their mixtures. Stenotrophomonas maltophilia E103 showed the best potential for metal uptake, accumulating the highest concentration of Pb2+ (29.0%) and Zn2+ (30.8%) in systems supplemented with single metals, while P. alcaligenes B101 and P. fluorescens C101 showed preference for the accumulation of Pb2+ (15.1%) and Cu2+ (23.8%), respectively. Although metal uptake decreased significantly in ternary metal systems, strains B101 and E103 maintained their preferences for Pb2+ in the ternary systems. The ability of these bacteria to metabolise spent engine oil with concurrent intracellular metal accumulation in the presence of high concentrations of Pb2+, Cu2+ and Zn2+ and their mixtures highlighted their potentials for use in the remediation of sites exposed to hydrocarbon-metal co-contamination.
KeywordsBiodegradation Heavy metal bio-uptake Pseudomonas Stenotrophomonas
We are grateful to the owners of the ARGs who allowed sample collection from their workshops and to Mr Femi Babalola of the Department of Chemistry and the Basel Convention Centre, the University of Ibadan who assisted in interpreting the GC-FID data.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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